CVE-2025-20718 is a stack overflow vulnerability classified under CWE-121, affecting the wlan AP driver in several MediaTek chipsets including MT6890, MT7615, MT7622, MT7663, MT7915, MT7916, MT7981, and MT7986. The root cause is an incorrect bounds check in the driver code, which allows an out-of-bounds write on the stack. This memory corruption can be exploited by a local attacker who already has user-level execution privileges on the device, enabling them to escalate their privileges to higher levels, potentially root or system-level. The vulnerability does not require any user interaction, increasing the risk of automated or stealthy exploitation. Affected firmware versions include SDK release 7.6.7.2 and earlier, as well as openWRT versions 19.07 and 21.02, which are commonly used in embedded wireless devices and routers. The CVSS v3.1 base score is 7.8, reflecting high severity with high impact on confidentiality, integrity, and availability. The attack vector is local (AV:L), with low attack complexity (AC:L), requiring privileges (PR:L) but no user interaction (UI:N). Although no public exploits have been reported yet, the vulnerability poses a significant risk due to the widespread deployment of these chipsets in consumer and enterprise wireless infrastructure. The issue is tracked internally by MediaTek as MSV-3581 and patched under WCNCR00419945, though no public patch links are currently available.

This vulnerability allows a local attacker with user-level access to escalate privileges on devices using the affected MediaTek chipsets. Such escalation can lead to full system compromise, allowing attackers to execute arbitrary code with elevated privileges, modify or exfiltrate sensitive data, disrupt device functionality, or create persistent backdoors. Given these chipsets are widely used in wireless access points and embedded devices globally, exploitation could affect network infrastructure security, leading to broader network compromise. The impact spans confidentiality (unauthorized data access), integrity (tampering with system or network configurations), and availability (potential device crashes or denial of service). Organizations relying on affected devices risk operational disruption and data breaches if the vulnerability is exploited. The lack of required user interaction and low attack complexity increases the likelihood of exploitation in environments where local user access is possible, such as multi-tenant or shared environments.

Organizations should monitor MediaTek advisories for official patches and apply them promptly once available. Until patches are released, restrict local user access to affected devices, enforce the principle of least privilege, and disable unnecessary local accounts or services that could be leveraged for exploitation. Employ network segmentation to limit access to management interfaces of devices using these chipsets. Regularly audit device firmware versions and upgrade to versions beyond SDK 7.6.7.2 or openWRT 21.02 when patches are integrated. Implement host-based intrusion detection to monitor for anomalous behavior indicative of privilege escalation attempts. For environments where firmware updates are delayed, consider deploying compensating controls such as application whitelisting or enhanced logging to detect exploitation attempts. Vendors and integrators should validate firmware integrity and consider additional hardening of the wlan AP driver code to prevent similar issues.